U.S. patent application number 10/106709 was filed with the patent office on 2003-02-27 for oxidative dehydrogenation of alkanes to olefins using an oxide surface.
This patent application is currently assigned to Conoco Inc.. Invention is credited to Budin, Lisa M., Meyer, Larry M..
Application Number | 20030040655 10/106709 |
Document ID | / |
Family ID | 26803934 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030040655 |
Kind Code |
A1 |
Budin, Lisa M. ; et
al. |
February 27, 2003 |
Oxidative dehydrogenation of alkanes to olefins using an oxide
surface
Abstract
A catalyst useful for the production of olefins from alkanes via
oxidative dehydrogenation (ODH) is disclosed. The catalyst includes
an oxide selected from the group containing alumina, zirconia,
titania, yttria, silica, niobia, and vanadia. The catalyst does not
contain any unoxidized metals; it is activated by higher preheat
temperatures. As a result, similar conversions are achieved at a
considerably lower cost.
Inventors: |
Budin, Lisa M.; (Ponca City,
OK) ; Meyer, Larry M.; (Ponca City, OK) |
Correspondence
Address: |
DAVID W. WESTPHAL
CONOCO PHILLIPS
P.O. BOX 4783
HOUSTON
TX
77210-4783
US
|
Assignee: |
Conoco Inc.
Houston
TX
|
Family ID: |
26803934 |
Appl. No.: |
10/106709 |
Filed: |
March 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60309427 |
Aug 1, 2001 |
|
|
|
Current U.S.
Class: |
585/627 ;
502/242; 585/629 |
Current CPC
Class: |
B01J 21/06 20130101;
B01J 21/066 20130101; C07C 5/48 20130101; C07C 2523/22 20130101;
C07C 2521/04 20130101; C07C 2523/10 20130101; C07C 11/02 20130101;
C07C 5/48 20130101; C07C 2521/08 20130101; C07C 2521/06 20130101;
B01J 21/10 20130101; C07C 2523/20 20130101 |
Class at
Publication: |
585/627 ;
585/629; 502/242 |
International
Class: |
C07C 005/09; C07C
005/327; B01J 021/12; B01J 021/14 |
Claims
What is claimed is:
1. A catalyst for use in oxidative dehydrogenation processes
comprising an oxide selected from the group consisting of alumina,
zirconia, titania, yttria, silica, niobia, and vanadia.
2. The catalyst of claim 1 wherein the oxide is essentially
zirconia.
3. The catalyst of claim 1 wherein the oxide is calcined at a
temperature in the range of about 500 to 1200.degree. C.
4. The catalyst of claim 3 wherein the oxide is calcined for 2-12
hours.
5. The catalyst of claim 1 wherein ethylene yield is at least
25%.
6. The catalyst of claim 1 wherein ethylene yield is at least
50%.
7. A method for the production of olefins comprising: heating an
alkane and oxidant stream to a temperature of approximately 500 to
700.degree. C. sufficient to initiate the oxidative dehydrogenation
of said alkane; contacting said alkane and oxidant stream with a
catalyst comprising an oxide; maintaining a contact time of said
alkane with said catalyst for less than 200 milliseconds; and
maintaining oxidative dehydrogenation favorable conditions.
8. The method of claim 7 wherein the oxidant is essentially pure
oxygen.
9. The method of claim 7 wherein the oxide is selected from the
group consisting of alumina, zirconia, titania, yttria, silica,
niobia, and vanadia.
10. The method of claim 9 wherein the oxide consists essentially of
zirconia.
11. The method of claim 7 wherein olefin production occurs in a
millisecond contact time reactor.
12. The method of claim 7 wherein ethylene yield is at least
25%.
13. The method of claim 7 wherein ethylene yield is at least
50%.
14. A method for converting alkanes to olefins comprising: heating
an alkane and oxidant stream to a temperature of approximately 500
to 700.degree. C. sufficient to initiate the oxidative
dehydrogenation of said alkane; contacting said alkane and oxidant
stream with a catalyst comprising an oxide; maintaining a contact
time of said alkane with said catalyst for less than 200
milliseconds; and maintaining oxidative dehydrogenation favorable
conditions.
15. The method of claim 14 wherein the oxidant is essentially pure
oxygen.
16. The method of claim 14 wherein the oxide is selected from the
group consisting of alumina, zirconia, titania, yttria, silica,
niobia, and vanadia.
17. The method of claim 16 wherein the oxide is essentially
zirconia.
18. The method of claim 14 wherein olefin production occurs in a
millisecond contact time reactor.
19. The method of claim 14 wherein ethylene yield is at least
25%.
20. The method of claim 14 wherein ethylene yield is at least
50%.
21. An oxidative dehydrogenation catalyst comprising an oxide
selected from the group consisting of alumina, zirconia, titania,
yttria, silica, niobia, and vanadia.
22. The catalyst of claim 19 wherein the oxide is essentially
zirconia.
23. A disposable oxidative dehydrogenation catalyst comprising an
oxide selected from the group consisting of alumina, zirconia,
titania, yttria, silica, niobia, and vanadia.
24. The catalyst of claim 23 wherein the oxide is essentially
zirconia.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of provisional
application Serial No. 60/309,427, filed Aug. 1, 2001 and entitled
Oxidative Dehydrogenation of Alkanes to Olefins Using An Oxide
Surface.
[0002] Statement Regarding Federally Sponsored Research or
Development
[0003] Not Applicable.
TECHNICAL FIELD OF THE INVENTION
[0004] This invention generally relates to the conversion of
alkanes to alkenes. More specifically, the invention relates to
employing oxidative dehydrogenation (ODH) to convert alkanes to
alkenes. Still more specifically, the invention relates to
non-metal catalysts used in ODH.
BACKGROUND OF THE INVENTION
[0005] In the commercial production of plastics, elastomers,
man-made fibers, adhesives, and surface coatings, a tremendous
variety of polymers are used. There are many ways to classify these
compounds. For example, polymers can be categorized according to
whether they are formed through chain-growth or step-growth
reactions. Alternatively, polymers can be divided between those
that are soluble in selective solvents and can be reversibly
softened by heat, known as thermoplastics, and those that form
three-dimensional networks that are not soluble and cannot be
softened by heat without decomposition, known as thermosets.
Additionally, polymers can be classified as either made from
modified natural compounds or made from entirely synthetic
compounds.
[0006] A logical way to classify the major commercially employed
polymers is to divide them by the composition of their monomers,
the chains of linked repeating units that make up the
macromolecules. Classified according to composition, industrial
polymers are either carbon-chain polymers (also called vinyls) or
heterochain polymers (also called noncarbon-chain, or nonvinyls).
In carbon-chain polymers, as the name implies, the monomers are
composed of linkages between carbon atoms; in heterochain polymers
a number of other elements are linked together in the monomers,
including oxygen, nitrogen, sulfur, and silicon.
[0007] By far the most important industrial polymers are
polymerized olefins, which comprise virtually all commodity
plastics. Olefins, also called alkenes, are unsaturated
hydrocarbons (compounds containing hydrogen [H] and carbon [C])
whose molecules contain one or more pairs of carbon atoms linked
together by a double bond. The olefins are classified in either or
both of the following ways: (1) as cyclic or acyclic (aliphatic)
olefins, in which the double bond is located between carbon atoms
forming part of a cyclic (closed-ring) or an open-chain grouping,
respectively, and (2) as monoolefins, diolefins, triolefins, etc.,
in which the number of double bonds per molecule is, respectively,
one two, three, or some other number.
[0008] Generally, olefin molecules are commonly represented by the
chemical formula CH.sub.2.dbd.CHR, where C is a carbon atom, H is a
hydrogen atom, and R is an atom or pendant molecular group of
varying composition. The composition and structure of R determines
which of the huge array of possible properties will be demonstrated
by the polymer.
[0009] More specifically, acyclic monoolefins have the general
formula C.sub.nH.sub.2n, where n is an integer. Acyclic monoolefins
are rare in nature but are formed in large quantities during the
cracking of petroleum oils to gasoline. The lower monoolefins,
i.e., ethylene, propylene, and butylene, have become the basis for
the extensive petrochemicals industry. Most uses of these compounds
involve reactions of the double bonds with other chemical agents.
Acyclic diolefins, also known as acyclic dialkenes, or acyclic
dienes, with the general formula C.sub.nH.sub.2n-2, contain two
double bonds; they undergo reactions similar to the monoolefins.
The best-known dienes are butadiene and isoprene, used in the
manufacture of synthetic rubber.
[0010] Olefins containing two to four carbon atoms per molecule are
gaseous at ordinary temperatures and pressure; those containing
five or more carbon atoms are usually liquid at ordinary
temperatures. Additionally, olefins are only slightly soluble in
water. Olefins have traditionally been produced from alkanes by
fluid catalytic cracking (FCC) or steam cracking, depending on the
size of the alkanes. Heavy olefins are herein defined as containing
at least five carbon atoms and are produced by FCC. Light olefins
are defined herein as containing one to four carbon atoms and are
produced by steam cracking. Alkanes are similar to alkenes, except
that they are saturated hydrocarbons whose molecules contain carbon
atoms linked together by single bonds. The simplest alkanes are
methane (CH.sub.4, the most abundant hydrocarbon), ethane
(CH.sub.3CH.sub.3), and propane (CH.sub.3CH.sub.2CH.sub.3). These
three compounds exist in only one structure each. Higher members of
the series, beginning with butane
(CH.sub.3CH.sub.2CH.sub.2CH.sub.3), may be constructed in two or
more different ways, depending on whether the carbon chain is
straight or branched. Such compounds are called isomers; these are
compounds with the same molecular formula but different
arrangements of their atoms. As a result, they often have different
chemical properties.
[0011] In the conversion of alkanes to alkenes, fluid catalytic
cracking and steam cracking (direct catalytic dehydrogenation
processes) are known to have their drawbacks. For example, the
processes are endothermic, meaning that heat is absorbed by the
reactions and the temperature of the reaction mixtures decline as
the reactions proceed. This is known to lower the product yield,
resulting in lower value products. In addition, coke forms on the
surface of the catalyst during the cracking processes, covering
active sites and deactivating the catalyst. During regeneration,
the coke is burned off the catalyst to restore its activity and to
provide heat needed to drive the cracking.
[0012] This cycle is very stressful for the catalyst; temperatures
are high and fluctuate and coke is repeatedly deposited and burned
off. Furthermore, the catalyst particles are moving at high speed
through steel reactors and pipes, where wall contacts and
interparticle contacts are impossible to avoid.
[0013] While it may be easy to dismiss catalyst damage and loss in
less expensive catalysts, the catalysts used in FCC and steam
cracking units are quite expensive. The expense stems from the use
of precious metals. For example, a typical supported metal catalyst
may cost in the range of $20-$40 per pound, of which the cost of
the precious metals may be between 50-80%. Thus, for a reactor that
uses 2 million pounds of catalyst, the total cost of the metals in
the reactor is considerable. Further, because FCC and steam
cracking units are large and require steam input, the overall
processes are expensive even before taking catalyst cost into
consideration.
[0014] As a result, because olefins comprise the most important
building blocks in modern petrochemical industry, the development
of alternate routes other than FCC and steam reforming have been
explored. One such route is oxidative dehydrogenation (ODH). In
ODH, an organic compound is dehydrogenated in the presence of
oxygen. Oxygen may be fed to the reaction zone as pure oxygen, air,
oxygen-enriched air, oxygen mixed with a diluent, and so forth.
Oxygen in the desired amount may be added in the feed to the
dehydrogenation zone and oxygen may also be added in increments to
the dehydrogenation zone. However, catalysts for oxidative
dehydrogenation are still being investigated and the development of
more effective catalysts for ODH is highly desirable.
SUMMARY OF THE INVENTION
[0015] The present invention provides a non-metal catalyst for use
in ODH. ODH was chosen for alkane dehydrogenation because it
overcomes thermodynamic limitations of olefin yield faced in direct
dehydrogenation and rapid coking of the catalysts resulting in
short catalyst life.
[0016] Although oxidative dehydrogenation usually involves the use
of a catalyst, and is therefore literally a catalytic
dehydrogenation, oxidative dehydrogenation (ODH) is distinct from
what is normally called "catalytic dehydrogenation" in that the
former involves the use of an oxidant, and the latter does not. In
the disclosure herein, "oxidative dehydrogenation", though
employing a catalyst, will be understood as distinct from so-called
"catalytic dehydrogenation" processes in that the latter do not
involve the interaction of oxygen with the hydrocarbon feed.
[0017] In accordance with a preferred embodiment of the present
invention, a catalyst for use in ODH processes includes an oxide
selected from the group containing alumina, zirconia, titania,
yttria, silica, niobia, and vanadia.
[0018] In accordance with another preferred embodiment of the
present invention, a method for the production of olefins includes
contacting a preheated alkane and oxygen stream with a catalyst
containing an oxide, sufficient to initiate the oxidative
dehydrogenation of the alkane (between 500-700.degree. C.),
maintaining a contact time of the alkane with the catalyst for less
than 200 milliseconds, and maintaining oxidative dehydrogenation
favorable conditions.
[0019] In accordance with an alternate preferred embodiment of the
present invention, a method for converting alkanes to olefins
includes contacting a preheated alkane and oxygen stream with a
catalyst containing an oxide, sufficient to initiate the oxidative
dehydrogenation of the alkane (between 500-700.degree. C.),
maintaining a contact time of the alkane with the catalyst for less
than 200 milliseconds, and maintaining oxidative dehydrogenation
favorable conditions.
[0020] In accordance with yet another preferred embodiment of the
present invention, an ODH catalyst includes an oxide selected from
the group containing alumina, zirconia, titania, yttria, silica,
niobia, and vanadia.
[0021] In accordance with still yet another preferred embodiment of
the present invention, a disposable ODH catalyst includes an oxide
selected from the group containing alumina, zirconia, titania,
yttria, silica, niobia, and vanadia.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The present invention relates to a non-metal oxide support
for converting alkanes to alkenes via ODH. Typically ODH catalysts
contain a precious metal, such as platinum, which promotes alkane
conversion. The present invention however, does not contain any
unoxidized metals; it is activated by higher preheat temperatures.
As a result, similar conversions are achieved at a considerably
lower cost.
[0023] In a preferred embodiment of the present invention, light
alkanes and O.sub.2 are converted to the corresponding alkenes
employing new oxide catalysts. Preferably, a millisecond contact
time syngas reactor is used. Use of a millisecond contact time
reactor for the commercial scale conversion of light alkanes to
corresponding alkenes will reduce capital investment and increase
alkene production significantly. Ethylene yield of 52% or higher is
achievable. This technology has the potential of achieving yields
above that of the conventional technology at a much lower cost. The
need for steam addition, as is currently required in the
conventional cracking technology, is eliminated by the present
process. However, in some embodiments, the use of steam is
preferred. There is minimal coking in the present process and
therefore little unit down time and loss of valuable hydrocarbon
feedstock. The novel catalysts improve the selectivity of the
process to the desired alkene. In addition, the carbon oxide
product produced at low levels is preferably primarily CO, not
CO.sub.2, and is thus more valuable for adjusting the syngas ratio
of H.sub.2/CO for possible use in Fischer-Tropsch processes.
[0024] The present catalysts are preferably in the form of foam,
monolith, gauze, noodles, balls, pills or the like, for operation
at the desired high gas velocities with minimal back pressure.
[0025] In some embodiments, ODH is carried out using the
hydrocarbon feed mixed with an appropriate oxidant and possibly
steam. Appropriate oxidants may include, but are not limited to
I.sub.2, O.sub.2, CO.sub.2 and SO.sub.2. Use of the oxidant shifts
the equilibrium of the dehydrogenation reaction towards complete
conversion through formation of compounds containing the abstracted
hydrogen (e.g. H.sub.2O, HI, H.sub.2S). Steam, on the other hand,
may be used to activate the catalyst, remove coke from the catalyst
via a water-gas shift reaction, or serve as a diluent for
temperature control.
[0026] Catalysts
[0027] In the present example, the catalysts were purchased from
Porvair Advanced Materials. Commercial products AL and PSZ46
correspond to product compositions Al.sub.2O.sub.3 and partially
stabilized ZrO.sub.2/MgO, respectively. The catalysts tested were
in the form of foam monoliths.
[0028] Test Procedure and Results
[0029] Once the catalysts were purchased, they were calcined at
500.degree. C. and tested in an atmospheric millisecond contact
time reactor for 20-30 milliseconds at 900,000 NL/kg/h.sup.GHSV
with a 10% nitrogen dilution and a molar fuel to oxygen ratio of
1.8. The results can be seen in Table 1 below.
1TABLE 1 Test Results for Oxide Supports Preheat Temp Ethane
Selectivity Ethylene CO H.sub.2 Catalyst (.degree. C.) Conv.
Ethylene CO H.sub.2 Yield Yield Yield AL 630 98.2 41.2 29.4 38.3
40.5 28.9 33.3 AL 660 96.9 47.8 27.1 31.0 46.4 26.3 30.0 PSZ46 525
94.9 55 30.2 35.2 52.2 24.1 33.4
[0030] Non-metal oxide supports produce ethylene yields comparable
to precious metal-containing oxide supports. While titania, yttria,
silica, niobia and vanadia were not tested, it is believed that
they will behave similarly to the alumina and zirconia samples.
Additionally, because the catalysts do not contain expensive metals
components, they will be fairly easy to dispose of.
[0031] Process of Producing Olefins
[0032] Any suitable reaction regime is applied in order to contact
the reactants with the catalyst. One suitable regime is a fixed bed
reaction regime, in which the catalyst is retained within a
reaction zone in a fixed arrangement. Catalysts may be employed in
the fixed bed regime using fixed bed reaction techniques well known
in the art. Preferably a millisecond contact time reactor is
employed. A general description of major considerations involved in
operating a reactor using millisecond contact times is given in
U.S. Pat. No. 5,654,491, which is incorporated herein by
reference.
[0033] Accordingly, a feed stream comprising a hydrocarbon
feedstock and an oxygen-containing gas is contacted with one of the
above-described non-metal oxide catalysts in a reaction zone
maintained at conversion-promoting conditions effective to produce
an effluent stream comprising alkenes. The hydrocarbon feedstock
may be any gaseous hydrocarbon having a low boiling point, such as
ethane, natural gas, associated gas, or other sources of light
hydrocarbons having from 1 to 10 carbon atoms. In addition,
hydrocarbon feeds including naphtha and similar feeds may be
employed. The hydrocarbon feedstock may be a gas arising from
naturally occurring reserves of ethane that contain carbon dioxide.
Preferably, the feed comprises at least 50% by volume light alkanes
(<C.sub.10).
[0034] The hydrocarbon feedstock is contacted with the catalyst as
a gaseous phase mixture with an oxygen-containing gas, preferably
pure oxygen. The oxygen-containing gas may also comprise steam
and/or CO.sub.2 in addition to oxygen. Alternatively, the
hydrocarbon feedstock is contacted with the catalyst as a mixture
with a gas comprising steam and/or CO.sub.2.
[0035] The process is operated at atmospheric or superatmospheric
pressures, the latter being preferred. The pressures may be from
about 100 kPa to about 12,500 kPa, preferably from about 130 kPa to
about 5,000 kPa. The process of the present invention may be
operated at temperatures of from about 400.degree. C. to about
800.degree. C., preferably from about 500.degree. C. to about
700.degree. C. The hydrocarbon feedstock and the oxygen-containing
gas are preferably pre-heated before contact with the catalyst. The
hydrocarbon feedstock and the oxygen-containing gas are passed over
the catalyst at any of a variety of space velocities.
[0036] Gas hourly space velocities (GHSV) for the process, stated
as normal liters of gas per kilogram of catalyst per hour, are from
about 20000 to at least about 100,000,000 NL/kg/h, preferably from
about 50,000 to about 50,000,000 NL/kg/h. Preferably the catalyst
is employed in a millisecond contact time reactor. The process
preferably includes maintaining a catalyst residence time of no
more than 200 milliseconds for the reactant gas mixture. Residence
time is inversely proportional to space velocity, and high space
velocity indicates low residence time on the catalyst. An effluent
stream of product gases, including CO, CO.sub.2, H.sub.2, H.sub.2O,
and unconverted alkanes emerges from the reactor.
[0037] In some embodiments, unconverted alkanes may be separated
from the effluent stream of product gases and recycled back into
the feed. Product H.sub.2 and CO may be recovered and used in other
processes such as Fischer-Tropsch synthesis and methanol
production.
[0038] In some embodiments the use of steam may be employed. As
mentioned above, steam may be used to activate the catalyst, remove
coke from the catalyst via a water-gas shift reaction (WGS), or
serve as a diluent for temperature control.
[0039] While the preferred embodiments of the invention have been
shown and described, modifications thereof can be made by one
skilled in the art without departing from the spirit and teachings
of the invention. The embodiments described herein are exemplary
only, and are not intended to be limiting. Many variations and
modifications of the invention disclosed herein are possible and
are within the scope of the invention. For example, the present
invention may be incorporated into a gas to liquids plant (GTL) or
may stand alone. Accordingly, the scope of protection is not
limited by the description set out above, but is only limited by
the claims which follow, that scope including all equivalents of
the subject matter of the claims. The disclosures of all patents
and publications cited herein are incorporated by reference in
their entireties.
* * * * *